Bistable nematic liquid crystal display devices generally require large electric potentials to initiate interstate switching between bistable states. One important reason for such large electric switching potentials is that sufficient electric energy must be supplied to each display cell for detaching and moving disclinations from pinning sites.
One embodiment of a nematic liquid crystal display device exhibits configurational bistability between two dissimilar states. See U.S. Pat. No. 4,333,708 issued to G. D. Boyd et al. on June 8, 1982. The two states, which exist separately in the absence of a holding potential, are topologically inequivalent and derive stability from disclination pinning. Interstate switching is accomplished by detaching and moving disclinations from a pinning site in response to an applied switching potential which exceeds a large, sharp switching threshold.
Reduction of the switching threshold level for this type of liquid crystal display device is achieved by prebiasing selected cells in the display with a small priming potential prior to applying the larger switching potential. See, for example, copending U.S. patent application, Ser. No. 411,305, filed Aug. 25, 1982. Although the switching threshold level is lower for the latter nematic liquid crystal display device, the switching level remains sufficiently high, for example, on the order of one hundred volts, to ensure detachment and motion of the disclinations necessary to achieve interstate switching.
In both of the above display devices, the problems of relatively large switching potentials and switching by disclination motion still exist.